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Wednesday, 20 March 2013

Nectar guide. Pollination and bees

This fine miscanthus is not pollinated by insects. Grasses are wind pollinated, as are conifers and many woody plants such as elderberry, (my own hay-fever bête noire). Wind pollinated plants have their own special strategies to ensure pollination. They produce prolific amounts of very small light pollen that is carried on the air. They frequently have separate male and female flowers, the latter with large receptive stigmas often held away from small leaves.

Birch catkins produce copious pollen before leaves appear and get in the way

Before you go out and dig up your grasses it is worth reflecting that pollinating insects require more from flowers than nectar. Bees have ‘pollen baskets’ to transfer protein rich pollen back to their broods and also collect waxes and other nutrients including stimulants as we will see. Bees are frequently observed visiting grasses to collect pollen. Many honeys have flavours of wind pollinated plants. A bee’s electrostatic charge can attract air born pollen which gets carried back to the hive.

These ethereal grasses are all wind pollinated

Most of our garden plants, are insect or animal pollinated. Apparently 200,000 different organisms provide this service worldwide. This pollination strategy usually involves attractively coloured flowers, nectar production, rich aromas and large sticky pollen. In many cases animals and plants have evolved in tandem as each make their own contribution to the efficiency of the joint venture - the transfer of pollen between plants and the provision of nutrition for the animal vector.

I use the terms ‘rich aroma’ and ‘attractive’ advisedly, the aroma may be foetid and the attraction visible to the insect and not to ourselves. Indeed some colours imparted in modern varieties by selective breeding might not be visible to the bees!

Bees are able to see ultra-violet colours invisible to ourselves.They are sensitive to colour at the blue, yellow, violet, end of the spectrum.They are not attracted to reds but other pollinators are. Bees perception of a flower is very different to our own as this link shows.

This picture would seem to belie my assertion that bees are not attracted to red. Could other attractions have seduced her, or is she seeing something different?

The bee does not see the dandelion asjust yellow

Most of us are familiar with nectar guides. These are the visible, or to us, sometimes invisible guides, for insects to find their nectar. From the plant’s perspective, it ‘wants’ the insect to be covered with pollen as it seeks nectar. Most of our plants have many different potential pollinators who might benefit from this flight directional service. Others have evolved very specific mutual exclusive arrangements. The survival of the ivy bee is completely dependent on ivy, although the ivy is not uniquely dependent on to the bee. Yucca’s relationship with the yucca moth is completely exclusive. Without each other, the yucca cannot set seed and the moth cannot breed.

If bees moved between different flowers in a completely random fashion, flowers would be cluttered with different plants’ pollen. Bees often display flower constancy where an individual bee remains loyal to his particular provider.

A basket of pollen

There have recently been two fascinating findings about pollination by bees.

Electrostatic charge

The New Scientist has recently reported research by Daniel Robert at the University of Bristol. Bees carry a positive electrical charge and flowers are negative. Bees appear to be sensitive to an electric field and it would seem that plants might have evolved to create a ‘bulls-eye’ shaped electrostatic field to guide bees to the pollen. It does appear that as a succession of bees visit a flower the plants electrostatic charge is depleted and so too the pollen. To paraphrase Daniel Robert the plant is saying to the bee, “ ignore my ‘come on’ signals, my electrics aren’t right, come back later!”

Bees’ pick-me-up

Caffeine might give bees a buzz. Thanks to National Geographic for this newly reported research by Geraldine Wright at Newcastle University and thanks for the pun! Research on the coffee plant and citrus shows how bees are attracted to the stimulant properties of caffeine in a plant’s nectar. From the plants point of view not only does it attract bees, it sharpens their faculties, so they remember where they have been!

I wonder if my calomondin orange flower acts as a stimulant

It is interesting to recall that many plants produce caffeine as a toxin to deter pests. Coffee is a particularly potent killer of slugs! As with many things in life, a little of what is bad for you might do you good. Nature ever so delicately, treads a very fine line.

22 comments:

The ones I find fascinating are flowers such as the bee orchid that exude female pheromones and mimic the look of a female in order to fool the male into pollinating the flower. I wonder whether the male ever realises that he has been fooled!

It's good to know that folk are looking back on old posts Fiona. When I started blogging I did not realise how accessible are old posts. I used to say that if my lectures stayed out of date long enough I would be at the forefront of horticultural technology as fashions and methods returned. I think its a bit the same with posts and its good to know that previous efforts are still valid. I think these new widgets that promote old posts are the best thing since sliced bread! By the way I am alerted if people comment on posts from the archive and I will respond to any matters raised. Lovely pictures like Harry's never date!

I have really enjoyed reading this fascinating post. In fact, I can't remember ever having learnt so much while eating curry at my desk! Thank you for updating me on the latest findings. I will now have a large coffee - it might help me remember where I was before I sat down to eat... I'm just grateful that I'm not a slug!

Tell your neighbour (Harry, is it?) he has captured some lovely shots Roger.I recently caught an old David Attenborough documentary on a similar topic on TV recently - it really did fascinate me and like your blog, helps us to understand how mother nature works.Science of any kind has never been my strong point and since taking up gardening, I now know why many schools are introducing gardening of sorts into the cirriculum - it makes the subject interesting.

Not quite sure Peter, perhaps someone might tell us of their experiences. There was quite a bit of publicity about this a couple of years ago. I like the image you conjure of offering slugs a cup of coffee!

This is a fascinating post indeed! I am also amazed that your neighbour is the photographer! Brilliant shots :) I remember a few years back some people at the allotment built a big polytunnel and they were going round telling everyone how stupid the old guy at the allotment was for asking "how will the bees get in".

Yes Harry is a brilliant photographer and his pictures often grace my posts, especially the ones relating to wildlife. I can only claim the first and last picture on this post!Yes the old boy you quote, was asking a very valid question about bees in protected structures. Depending on the openings into the structure bees may or may not pollinate the plants inside. Often not, although for some indoor crops such a strawberries, growers introduce bees. Another strategy is to grow crops such as climbing french beans that do not require insect pollination. I am trying this year to get some early beans from the new hybrid between french bean and runner bean -it is self pollinated. I will be sowing a couple of pots in my heated conservatory any time soon with a view to moving them on in very large pots in my cold greenhouse.

Hi, I am new to your blog and looked around at previous posts before commenting. I too have hawk visitors, but the crows are the ones terrorizing my cockatoo. I can see why Poppy was not pleased with a hawk visit. We get many hawks here in Niagara Falls as I live within walking distance of the Falls. There are lots of places for hawks to hunt and live at the Niagara Gorge. Crows come to Creem Cheez's window and a screaming battle ensues. I am sure they scream racial remarks at each other, one species white and the other black. My cockatoo also says very mean things to them, like get the blank out of here. I did not teach him that, my husband did.

I also have posted on new bee findings and get my information from Science, where I am a member. I love your neighbor's photographs. He is a real artist with the camera.

And you are a real artist with a camera yourself. I have just visited your site and anyone who has enjoyed my post on bees should hop over to your site to read some more about bees. They say great minds think alike choosing the same topic for their current post!

Fascinating post, Roger. (So nice to "meet" you, BTW.) I did a post last Summer on our growing bumble bee population in Utah. My research on the subject fueled my desire to know more. Bees are indeed a fascinating little creatures. Your information was a delightful read.

Thanks for reinforcing the point about ultra violet, making clear what I intended to say Emily! I have checked on your own blog and left a comment to say hello! If readers follow the link in my blog "this link" it takes you to a picture of a dandelion with a photographic representation with what a bee might see in ultra violet.